Alan R. Hale: Sport Optics (Hale Optics, 2013)
Great overview on choosing and using binoculars, spotting scopes and rifle scopes. Gives you all the necessary information for selecting the perfect optics for your purposes.
Philip S. Harrington: Touring the Universe through Binoculars (John Wiley & Sons, New York, 1990)
Probably the most comprehensive book ever written about astronomy with binoculars. Contains hundreds of objects that can be observed on the northern and southern skies, but unfortunately no star maps.
Craig Crossen, Wil Tirion: Binocular Astronomy (Willmann-Bell, Richmond, 1991)
Comprehensive book, but with fewer objects than Harrington‘s book. Includes Wil Tirions The Bright Star Atlas.
Robert Burnham, jr.: Burnham’s Celestial Handbook (Dover Publications, New York 1978)
Very extensive, three-volume work. Was written for telescopes, but provides a lot of background information about the visible objects. Unfortunately, the data are partly outdated now.
Craig Crossen, Gerald Rhemann: Sky Vistas (Springer, Vienna 2004)
Richly illustrated book about objects for binoculars and rich-field telescopes. It is similar to Craig Crossens Binocular Astronomy, but more extensive and gives insight into the structure of our galaxy.
Rudolf Brandt, Bernd Müller, Eberhard Splittgerber: Himmelsbeobachtungen mit dem Fernglas (Harri Deutsch, Thun 1984)
This book contains much theory and lot of background knowledge about optics. Worth reading, but aims less to an observer. Slightly dated, but still worth reading if you can read German.